Assessing the effects of the Prestige oil spill on the European shag (Phalacrocorax aristotelis): trace elements and stable isotopes

Sanpera, C., Valladares, S., Moreno, R., Ruiz, X. & Jover, L. Assessing the effects of the Prestige oil spill on the European shag (Phalacrocorax aristotelis): trace elements and stable isotopes. Science of the total environment 407, 242–249 (2008).


The Prestige oil spill resulted in the mortality of several seabird species on the Atlantic NW coast of Spain. Shag casualties were particularly relevant, since populations are resident in the area the whole year round and because of several features which make them highly vulnerable to environmental hazards. Ecological catastrophes give us the opportunity of collecting samples which, otherwise, would be difficult to obtain. We examine the potential of shag corpses as bioindicators of inorganic pollution and the possible factors of variability, such as biological traits (sex, age) or nutrition status. We determined trace elements (Hg, Se, Cr, Pb, Zn and Cu) and isotopic signatures (15N, 13C) in soft tissues (muscle, liver) and in primary feathers formed at different times (before and after the Prestige) in individuals of known sex and age, collected at the time of the Prestige disaster. These were compared with data from another group of shags trapped accidentally in fishing gear in 2005. Our results did not seem to be affected by sex or age on any of the analysed variables. The higher nitrogen isotopic signatures in  the soft tissues of the Prestige shags may be related to the nutrition stress caused by a poorer body condition,which is also reflected in increasing levels of some metals in the liver.This isotopic enrichment was also observed in newly forming feathers when compared to the old ones. On the other hand, the lower δ15N and Hg values in shag feathers from2005 point to a shift in feeding resources to prey of lower trophic levels.We found that feather features (being an inert tissue and having a conservative composition), if combined with careful dating and chemical analysis, offer a very useful tool to evaluate temporal and spatial changes in seabird ecology in relation to pollution events.

A three-isotope approach to disentangling the diet of a generalist consumer: the yellow-legged gull in northwest Spain

Moreno, R., Jover, L., Munilla, I., Velando, A. & Sanpera, C. A three-isotope approach to disentangling the diet of a generalist consumer: the yellow-legged gull in northwest Spain. Marine Biology 157, 545–553 (2010).


The widespread omnivory of consumers and the trophic complexity of marine ecosystems make it difficult to infer the feeding ecology of species. The use of stable isotopic analysis plays a crucial role in elucidating trophic interactions. Here we analysed d15N, d13C and d34S in chick feathers, and we used a Bayesian triple-isotope mixing model to reconstruct the diet of a generalist predator, the yellow-legged gull (Larus michahellis) that breeds in the coastal upwelling area off northwest mainland Spain. The mixing model indicated that although chicks from all colonies were fed with a high percentage of fish, there are geographical differences in their diets. While chicks from northern colonies consume higher percentages of earthworms, refuse constitutes a more important source in the diet of chicks from western colonies. The three-isotope mixing model revealed a heterogeneity in foraging habitats that would not have been apparent if only two stable isotopes had been analysed. Moreover, our work highlights the potential of adding d34S for distinguishing not only between terrestrial and marine prey, but also between different marine species such as fish, crabs and mussels.

Ten Years after the Prestige Oil Spill: Seabird Trophic Ecology as Indicator of Long-Term Effects on the Coastal Marine Ecosystem

Moreno, R., Jover, L., Diez, C., Sardá, F. & Sanpera, C. Ten Years after the Prestige Oil Spill: Seabird Trophic Ecology as Indicator of Long-Term Effects on the Coastal Marine Ecosystem. PLoS ONE 8, e77360 (2013).


Major oil spills can have long-term impacts since oil pollution does not only result in acute mortality of marine organisms, but also affects productivity levels, predator-prey dynamics, and damages habitats that support marine communities. However, despite the conservation implications of oil accidents, the monitoring and assessment of its lasting impacts still remains a difficult and daunting task. Here, we used European shags to evaluate the overall, lasting effects of the Prestige oil spill (2002) on the affected marine ecosystem. Using δ15N and Hg analysis, we trace temporal changes in feeding ecology potentially related to alterations of the food web due to the spill. Using climatic and oceanic data, we also investigate the influence of North Atlantic Oscillation (NAO) index, the sea surface temperature (SST) and the chlorophyll a (Chl a) on the observed changes. Analysis of δ15N and Hg concentrations revealed that after the Prestige oil spill, shag chicks abruptly switched their trophic level from a diet based on a high percentage of demersal-benthic fish to a higher proportion of pelagic/semi-pelagic species. There was no evidence that Chl a, SST and NAO reflected any particular changes or severity in environmental conditions for any year or season that may explain the sudden change observed in trophic level. Thus, this study highlighted an impact on the marine food web for at least three years. Our results provide the best evidence to date of the long-term consequences of the Prestige oil spill. They also show how, regardless of wider oceanographic variability, lasting impacts on predator-prey dynamics can be assessed using biochemical markers. This is particularly useful if larger scale and longer term monitoring of all trophic levels is unfeasible due to limited funding or high ecosystem complexity.

Influence of trophic ecology and spatial variation on the isotopic fingerprints of seabirds

Moreno, R., Jover, L., Velando, A., Munilla, I. & Sanpera, C. Influence of trophic ecology and spatial variation on the isotopic fingerprints of seabirds. Marine Ecology Progress Series 442, 229–239 (2011).

Notwithstanding the potential applications of stable isotopes in feeding and migration studies, the simultaneous influence of diet, foraging behavior and spatial variation on the stable isotope signatures of seabirds is poorly understood. Many studies have interpreted their isotopic signatures without considering local baseline and prey isotopic signatures; consequently, the main factors causing isotopic differences between populations have frequently not been discerned. To examine the influence of these factors on the stable isotopic signatures of seabirds, we analyzed the δ15N, δ13C, δ34S and Hg concentrations of chick feathers of the European shag Phalacrocorax aristotelis, its main fish prey and baseline indicator organisms (mussels), all sampled in 2 sectors of northwest coastal Spain with marked differences in primary productivity. Our results show that the δ15N signature and Hg concentration of shags are influenced by both feeding ecology and spatial variation. The δ13C and δ34S signatures, however, mainly related to spatial differences and can thus be used as reliable geographic markers. Our findings also highlight the importance of assessing spatio-temporal variation in baseline isotopic signatures and their progressive
integration through the food web. Omission of potential prey and baseline values, or application of only a single baseline to the food webs of the 2 sectors, assuming isotopic homogeneity because of geographical proximity, would have led to significantly distorted interpretations of feeding ecology of shag chicks.